Airway traffic control system



May 2?, E947. 1s. N. www ET Al.

AIRWY TRAFFIC CONTROL SYSTEM 5 Sheetsfheet l Filed Jan. 21, 1943 OMMO(v. nventcr mwgh-t and 0.5mm a THEIR Gtorucg S. N. WRGHT ETAL AIRwAYTRAFFIC CONTROL SYSTEM Filed Jah. 21, 1945 3 sheets-sheet 2IIIIIIIIIIIIIII-llllll llilllllllllllllllllllllllllliillll E?, E94?. s.N. wlan-rr Erm. A

mmm' TRAFFIC common sYs'rEM Filed Jan. 2l,- 1943 3 Sheets-Sheet 3Patented l www: invention relates to c '1-r -r" its. thi) ident-'imm m'thealtitude of airplanes.

l mchaixplanes w travel over spediled ma rm at ied altitudes on variousstretches it is essential that the whereabmzts of airplanes alreadygiven authorization to m in the vicinity be definitely known.l Althoughpilots of airplanes living over commercisl air routm are seldom lostbecause radio range legs or courses guide them over the grolmdy route,radio mes and radio ian markers inform them when tmy have reachedcertain cheek- Doints or stations along the air route and altimetersinform them of their altitude,` there is a possibility that a pilot maynot know what radio il" he is passing over. For reasons of safety, theshould be iniormed of the location, identity and altitude of eachairplane by meellenica: and electrical apparatus automatically so thatwrong indications or reports due to failure of the human element areavoided.

In view of the foregoing and other considerations. it is proposed inaccordance with the present invention to pmvlde apparatus. at each radioiin, check-point or ground location, which by radio commmiostingapparatus will communicate with airplanes yins over auch particularcheck-point only at one altitude at a time. so that if a plurality ciairplanes ily over the same check-point at diflerent altitudes. as ispossible,

such radio can be established with only one i i at a time, therebyavoidins the possibility or a mutilated code or other interierence.

More specically, it is further proposed to mit the information, ofairplane identity. airplane altitude and check-point identity. from suchcheck-point location to a centralised dispetchers omce and to tmretransmit informae at which he is living and is mins over, so that theme entr-soins pilot not only has the check-point speciiically dlspatcnmgof airplane traine. bv

(Ci. rfb-$58) asecondtime duringasingleiilshtoverthe check-point orother ground location.

Another object oi. the pmt invention resides in utilizing thecheck-point located apparatus for transmitting the answer-bach messagethe central omce to the pilot of the airplane.

Another object oi the present invention resides i'n the provision ofmeans for preventing the check-point located apparatus fromcommunicating with a second airplane until the complete answer-backinfomation for a first airplane has been transmitted from the centralomce back to the pilot of such airplane.

Another object o! the present invention resides in the provision oimechanism at the check-point ground location for determining which oneof a plurality of airplanes flying at different altitudes over auchlocation at the same time shall be first to communicate with thedispatcher-'s .omce through the medium of the check-point ground locatedapparatus.

Another object oi the present invention resides in the plovlfslon ofcode creating, code repeating,-and decoding mechanism for transmittingby code the aforementioned information between the airplane and thedlpatchers ollloe.

Other objects. purposes and characteristic features o: the presentinvention will in part be pointed out in the speciiication hereinafterand will in part be obvious from the accompanying drawinssinwhich:

Figs. 1A and 1B show the airplane carried apparatus, the apparatuslocated at a check-point and a portion of the apparatus located at thedlspatchers olllce: and

Fig. 2 shows a time chart illustrating the sequenoe of operation oi thevarious devices oi the apparatus illustrated in Figs. 1A and 1B.

Structure.Referring-to Fiss. 1A and 1B of the drawings, apparatus hasbeen illustrated therein to show one embodiment of the present inventionwhich apparatus is located at three different places, namely. on theairplane designated "Plahe by suitable legend, at the checkpointlocation CPS, shown by dotted lines, and at the central oilice ordispatcher's olilce DO also shown by dotted lines. On the airplane. asillustrated, are shown a pilot's radio transmitterreceiver PIR. whichai'l'ords direct two-way radio communication between the pilot and thedispatcherc oillce or some operator under the dispatcher's Jurisdiction,and in addition to this pilots radio PIR therein provided an airplanereceiver PR and an airplane transmitter PT for the' purpose ofautomatically communicating fioul.

scenico i which is derived through the noch contect if the relay OCR?.These of tedio carrier 'requency energy have superimnosed thereon, hatis, are modulated ny tone frequencies eenerated by the tone generators2T to 21T inclusive, )ne at e, time. That is, e tone pulse comesooncl-,mz to tone generator 2T is mst emitted by the interina, ATisuperimposed of course unen the :entier frequency, which is thenfollowed by tone puke and then by tone pulse d, end so on un-u ill ellof the tone pulses 2 to il have been transnltted, after which this cycleis repented.

Let us now essunie that the dirplane Plane (see Fie. iii) gets withinthe renee of the radio :eem transmitted by the ent/enne, ATi, it beinginderstoocl that the radio frequency is such and ;he antenne. sodesigned that this radiation 4of redio waves by the antenne AT5 isdirected meinm ly upwardly through e, limited angle of spread so that enairplane must he almost directly over u the check-point in order torespond to the ref :listed energy. Thot is, in practice, the airplaneremains in communication with the check-point apparatus only for aboutone-half minute during its flight over the check-point.

Let us now assume that the airplane Plane is dying at an altitude of2G00 feet end that its eltimeter contact il is in engagement with ste.-tionary Contact 2 of the altimeter .elli/I. Under this condition theeirplane receiver PR is receptive only if rudio Waves of the properirequency are emitted by the antenne ATi and then only ii they aremoduleted at the rate oi modulation effected by tone generator 2T. Onthe next rotation of the scanning Contact iii when it reaches thestationery contect of he altitude scanner AS, the energy transmitted bythe transmitter CPT through the medium of the antenna ATi to thereceiver PR will cause the relay TR carried by the airplane Plane topick up and by the closing of its front Contact dil closes en energizingcircuit for the motor This causes the motor M3 tc operaie and close s.sticlr circuit for the stick relay TRP including the commutator contactsPCi and stick Contact li. Rotation of the coding cem PC3 in aclockwisedirection results in the closure of Contact i@ of the eirplanetransmitter PT which results in the transmission of radio frequencyenergy impulses from the antenna ATS to the antenne ATli resulting inthe picking up oi' the relays CR and SR. The picking up of the relay ESRcloses its front com tact 33 thereby energizing the loch. :relay LR andcausing the latch wheel LW to be held in its contact 2 position by thelatch iii, in which position the rotary erm 2E! still engages the ste.-tionary contact segment 2 of altitude scanner AS. Energization of theloci: magnet LR by the opening of its Contact 2li. of course deenergizesthe clutch magnet CM and removes the application oi torque to thescanning shaft .22. It is thus seen that the clieclpoint apparatuscontinues to transmit radio frequency energy modulated at the same rateas before from the transmitter CPT to the receiver PR on the airplane.

Referring now to Fig. 2 the picking up of the relays TR and T'RPP on theairplane is indicated by the rise in graphs 62 and 53 whereas thepicking up of the relays CR and SR and the energization of the lockmagnet LR is indicated 'by the rise in graphs f, B5 and 55,respectively. The relay CR will of course follow the code transmitted bythe coding cam C and this code consists of four impulses followed icythree irnpulses followed by two immusee es indiceted by r PCi reclose.

the humos on coding wheel and. icy clashes in Fien 2 or the drawingsThis codo receivingf reley CR then repeats these impulses through themedium oi? its contact by intermittent energization of 'the code receiving relay GCR located in the dspetchers cnice DO. It will he seen thatthis code receiving reley CCR through the medium of its front con tactsdi will cause the received code to he retransmitted to the ciro-iene hythe intermittent energization of the relay @CRP ond the intermitteiltopening of its loool; conte ,t 38, which Contact ri feeds tone energy tothe radio trains mitter CPT. In other words, es indicated by graph t2 inFig. Z of the drawings the code transmitted by the airplane to the oiiceis repent/ed beck to the airplane by en o' period for erich on" periodof the ground located releys es shown by graphs trl, 'lli and EiBrepresenting the relays CR, OCR and @CRP in Fie. 2 of the drawings.

Let us now observe more speciiicelly how the coding motor M3 on theairplane is energized end how it is deeners'ized after the coding cemhas made one complete revolution. Referring to Fig. lA the originelpicking up of the relay TR causes energy to loe applied through thelinediurn of its frontcontact Bil through e circuit including the motorM3 and 'the front contect l@ of the relay TRP. As soon es the codingshaft has turned through a small angle, end before the slow droppingrelay TRP has had en opportunity to drop, the commutator contacts lYCiand PC2 are both closed thereby closing d stiel-r circuit for the relayTRP including the contact PCi and also including the sticlr contact ilof the relay TRP. The motor Mil is now also energized through another orauxiliery circuit cludine the front contact lil of the relay TR? andincluding the commutator contact PCT?. This auxiliary circuit for themotor iiil is provided so as to cause continuous operation of the `motorM3 in spite of intermittent deenergization and dropping of the relay TR.

The relay TRPP is energized each time thet the relay TR is picked up andis also energized so long es the motor Mt is energized, so thatthisrelay TRPP will assume its energized position as soon as the codingmotor M3 is initiated into operetion und will remain either continuouslyor intermittently energized until the relay TR is permanentlydeencrgizcd. This relay TRP? is so slow dropping that it will not dropits contacts after complete deenergizetion of its windings uil-- tilabout one-half minute of time has elapsed. In practice this cannot bereadily done by u relay of the ordinary construction and a specialtiming relay including a dash-pot or other suiteble time delay means maybe employed, if desired. When the motor has operated the coding WheelFC3 through its entire revolution the Stich circuit for the relay isbroken et the commutator contacts PCi thereby causing deenergization ofthis relay TRP and causing deenergizaition o the motor M3 before thecontacts The relay TRP will not seein. he picked up until the slowdropping relay TRP? has assumed its dcenergized position, which requiresabout one-half minute, this by reason of the fact that the nich-upcircuit for the relay TRP includes the beck. contacts i3 of the relayTRPP and. lf3 of the relay TF, in series. In prectice, as alreadypointed out, en airplane is not within the radiating range of 'thetransmitter CPT et e, checisqioint for more than about helrninute andsince the slow dropping rele-y 'Ii'RPlP d requires about a half-minuteperiod to be operated to its deenergized position the airplane apparatusof a particular airplane can only get into communication once during aflight over a checkpoint radio transmitter.

Referring again to Fig. 2 of the drawings time has now elapsed asindicated by the nine dashes 58 representing the airplane identifyingcode and this code has not only been transmitted to the dispatchers omceas indicated by the jcgged graph till signifying the operation oi therelay CR and received at the dispatchers orilce as illustrated by thelogged graphs lil and et illustrating the operation oi the codereceiving relays OCR and OCRP located in the dispatchers oce andcheckpoint respectively, but has also been retransmitted baci: to theairplane as indicated by the joggecl graph t2, signifying the operationoi the relay Tft constituting part of the receiver PR located on theairplanePlane. This code is repeated into the pilot's earphone PHSthrough the medium of contact i5 of the relay TR.

Referring again to Fig. 2 it will be observed that altitude relay A2 hasnow been energized as indicated by the graph ill and that the picking upof its contact 23 has caused deenergization of the relay AP. However, byreason of its slow dropping characteristic, as indicated by the shadedportion of the graph ll, this relay AP has not yet assumed itsdeenergized position. Dropping of the stick relay TRP has, however,taken place and this is indicated by shaded portion ci the graph lil ofFig. 2 of the drawings. In regard to the picking up of an altituderelay. such as the relay .A2, this relay is slow to piclr up, asconveniently indicated, and will not nichF up during rotation of thecontact arm 2b but will piclr up if this contact arm stops on one of thestationary contact segments,

As thus far described the check-point located apparatus Cris has scannedthe area directly above this location, and has found an airplane iiyingat the u@ foot altitude, causing the scanner to stop on the contactsegment 2 and resulting in the reception oi radio Waves by the air planehaving e. tone signifying the 20D() foot altitude superimposed thereon.This resulted in the lock, magnet LR being magnetized which caused theapparatus on the airplane Plane to transmit a plane identifying codeconsisting of four impulses followed by three impulses, followed by twoimpulses and the coding apparatus on the airplane has completed itscycle and has again been brought to a stop,

As already pointed out the relay AP is very slow dropping, as indicatedby the heavily shaded portion of line lll, and was held up throughoutthe entire transmission of the airplane identifying code to thedispatchers oce and back to the airplane. This relay AP has now reachedits deenergized position as a result of which its back contact El hascompleted an energizing circuit through the motor Mt and including thefront contact til of the stick relay APP. As soon as the motor M2 hasoperated the coding shaft bil through a small angie a stick circuit forthe relay APP is closed including the back contact 2l of the relay AP,the commutator contact CPC and the stick contact 2t? oi this relay APP.The motor Mt will nowcontinue in operation until the coding shaft tu,driven through suitable gears (not shown), has completed one completerevolutlon at which point the stiel; circuit for the relay APP is brokenat the commutator contact CPC. During this revolution of the codingshaft i3@ the radio fix coding cam CPF', ior identify the radio hx orchecl-point at which it is local will transmit code elements to identifyt check-point, which consists ci four pulses in present instance. rThisis followed by a series pulses identifying the altitude at which the aplane is ilying, which in the present instance ci sists of two pulses,wul be transmitted by i coding cam CP2 because the altitude relay nowassumes the energized position and ali the other altitude relays Ai-Ailassume their i energized positions.

It will be observed that the humps on the c ing cam CP2 do not overlapwith the humps the coding cam CPF sc that the four impul` created by thecam CPF will be followed by i two impulses created by the coding camCP2. T code will cause intermittent picking up and dr( ping of the codefollowing relay GCR, in the d patchers ofllce BO through a circuit whichm be traced from the positive terminal of a sou; of current throughbaci; contact 223 of the rei AP and ythrough thc contact CF controlledthe coding cam CPF and through a multi; branch circuit also includingthis back cont-z 2d of relay AP and front contact 25 of relay andfurther including the contact C2 of the cc ing cam CP2 and from there onthese two multi; circuits converge into one circuit including i linewires 3l and the code following relay O( located in the dispatchersoirice. This code co ,sisting of a group oi four impulses identifyi theradio x, followed by a group of 'two impuls identifying the altitude atwhich the airplane ilying, is indicated by the dashes 59 in Fig. 2 thedrawings. it will be observed that these cc impulses result incorresponding picking up a: dropping of the relays OCR and OCRP as shoiby the graphs l5 and El? of Fig. 2 and is also i dicated bycorresponding oil periods in the e ergizing circuit for the relay TR asindicated the graph t2 in Fig. 2 of the drawings.

Referring to Fig. iB it will be observed tl". the code transmitted from'the airplane to the d patchers ofiice and consisting of an airplane idetiilcation code cannot overlap or interfere wi the code transmitted bythe coding cams Cl and CP2 because the lrst of these codes is trarmittecl through a circuit including the front co tact 2d of the relay APwhereas the second me tioned code is transmitted through a circuit icluding the contact 28 in its deenergized po tion.

Referring now to the graph it in Fig. 2 of t drawings, this graph showsthat the relay Ol was picked up in response to the ilrst code i1 pulsetransmitted to the dispatchers omce manifested by the relay OCR and wasnot dropp until the last element of the complete code h beentransmitted, and that the relay K controll by this relay ODC repeatsthis same operation the check-point location. This is shown in Fig bythe graph ill. By referring to Fig. 2 it will observed that theapparatus at the check-poi and on the airplane is not returned to its ncmal condition immediately after the entire co has been retransmitted tothe airplane ev though the apparatus located in the dispatche cnice is.This is due to the fact that the pa ticular altitude code which wasassumed to ha been transmitted was a two-impulse code sigr tying analtitude of 20ml feet and for this reas the coding shaft il@ had notcompleted its rot tion and this idle rotation ci' the shaft Si is inclradio transmitting apparatus located at the check-point or radio nxlocation.

It should also be understood that, ii desired. instead of having theairplane receiver PR rendered responsive only to radio transmission of aparticular radio frequency modulated to a particular tone that thisresponse may be through the medium oi particular radio frequenciesalo'ne and irrespective oi tone current modulation. The tuning of thereceiving apparatus PR would be accomplished in this case through themedium or' a contact similar to the contact il on the alti meter. Inother words. instead of using one radio carrier frequency and aplurality of tone irequencies a plurality oi radio carrier frequencieswithout having a tone frequency superimposed thereon may be employed, ifdesired. Since the conventional showing would be the same no additionaldrawings are deemed necessary.

The applicants have thus shown and described one particular embodimentand slight variations of their invention and one manner in which theirinvention may be employed, and have disclosed this invention in amore orless conventional manner. It is therefore desired to be understood thatthis has been done because radio communicating apparatus is well-knownin the art and detailed circuits and apparatus including amplier,rectifier and detector tubes are so well known in the art that speciilcdisclosure thereof is considered and believed unnecessary and it shouldbe understood that the particular apparatus shown and described has beenselected to show the nature of the invention and has not beenillustrated to show the exact construction preferably employed inpracticing the invention and it should be understood that variouschanges, modifications and additions may be made in practising theinvention, so long as these changes come within the scope of thefollowing claims.

What is claimed as new is:

1. In combination with ground station located radio transmittingapparatus, of means operatvely coupled to said radio transmittingapparatus for successively emitting radio beams characterizing differentaltitudes, airplane carried radio receiving apparatus having tuned meansadjusted to respond to such radio beams one at a time, and altituderesponsive means operatively coupled to said airplane carried radioreceiving apparatus for adjusting said tuning means of said radioreceiving apparatus to respond only to a radio beam characterizing thealtitude such airplane is flying at at thattime.

2. In combination with ground station located radio transmittingapparatus, of means operatively coupled to said radio transmittingapparatus for successively emitting radio beams characterizing differentaltitudes, airplane carried radio receiving apparatus having tuned meansadjusted to respond to such radio beams one at a time, altituderesponsive means operatively coupled tosaid airplane carried radioreceiving apparatus for adjusting said tuning means oi said radioreceiving apparatus to respond only to a radio beam characterizing thealtitude such airplane is flying at at that time'l and means to causesaid radio transmitting apparatus to continue for a limited time to emita radio beam liti characterizing a particular altitude if the airplanecarried radio receiving apparatus has been adjusted by said altituderesponsive means to such altitude adjustment and has responded to theinitial radio beam characterizing such altitude.

3. In combination, a central oiice, a ground station, an airplanecarried apparatus, code creating means included in such airplane carriedapparatus for transmitting by radio a code identifying such airplane,code creating means at such ground station having its operation governedby transmission of said airplane identifying code for generating a codeidentifying such ground station, communicating means controlled by saidcode creating means for transmitting both of such codes over line wiresto said centrai oiice in non-overlapping succession, and radiocommunicating means for retransmtting over a distinctive channel both ofsaid codes from said central oiiice to said airplane carried apparatus.

4. The combination of interrelated radio transmitting apparatus at acheck point ground station and radio receiving apparatus carried by anairplane, interrelated radio transmitting apparatus on said airplane andradio receiving apparatus at said ground station. of means including theradio transmitting apparatus at said ground station for successivelyemitting radio beams characterizing different altitudes, airplanecarried altitude responsive means for adjusting the airplane carriedradio receiving apparatus to render it responsive to a radio beamemitted by the ground station located radio transmitting apparatuscharacteristic of the altitude the airplane is -flying at at that timeas manifested by such altitude responsive means, means responsive to thereception of a radio beam initiated by said airplane carried radioreceiving apparatus and emitted by the airplane carried radiotransmitting apparatus and received by the radio receiving apparatus atsaid ground station for causing the radio transmitting apparatus at suchground station to continue to transmit the last transmitted radio beamfor a predetermined period of time, and means on said airplane fortransmitting information to such ground station identifying saidairplane through the medium of the radio transmitting apparatus on saidairplane and the radio receiving apparatus at said ground station duringsaid period of time.

5. The combination of interrelated radio transmitting apparatus at acheck point ground station and radio receiving apparatus carried by anairplane, interrelated radio transmitting apparatus on said airplane andradio receiving apparatus at said ground station, of means including theradio transmitting apparatus at said ground station for successivelyemitting radio beams characterizing different altitudes, airplanecarried altitude responsive means for adjusting the airplane carriedradio receiving apparatus to render it responsive to a radio beamemitted by the ground station located radio transmitting apparatuscharacteristic of the altitude the airplane is ying at at that time asmanifested by said altitude responsive means, means responsive to thereception of a radio beam initiated by said airplane carried radioreceiving apparatus emitted by the airplane carried radio transmittingapparatus and received by the radio receiving apparatus at said groundstation for causing the radio transmitting apparatus at such groundstation to continue to transmit the last transmitted desinee o beam fore. predetermined period oi time, ns on seid sirmione for transmittingintorion to such ground station identifying sold iene through the mediumci the radio trousing apparatus on seid airplane ood tice recio ivinooppcrotus et seid ground station dursuch predetermined time. sind meanset seid 1nd stetion for tlirough the medium oi seid um station locatedradio transmitting sono is and scid eirplane ,carried redio receivingaretus trensrnittins,J inforniotion identifying round station. incomblnotion, e ground stotion loceted lo transmitting opperetus, eground station Yted radio receiving apparatus, airplane cor redioreceiving e-nperdtus and airplane :led rudio transmitting apparatus, ofineens 11s-.tively associated with. seid ground station ted tediotreinsmitting apparatus i'or ecus such apparatus to successively emitsoffice lotions each characteristic ci e, different eltie, airplaneccrried menos including scid airie carried receiving oppor-ctms forcousine the ratively associated eirpiene corrieri space lotiontransmitting apparatus to transmit o ce radiation when the operativelyassocieted :lane corrieri radio receiving apparatus reres o spacercdietion characteristic oi the sitie the airplane is theo flying ot,end ground ited code communicating apparatus for transting to o distantpoint o code chorocteristic that altitude in response to the receptionof ce radiation by the ground located radio re- ,fing apparatus fromsuch airplane corried io transmitting apparatus. in e, system i'orautomatically reporting the entre and identity of airplanes flying overe. und station; equipment on eec'n. airplane in- :ling radiotransmitting means, e code senddevice and means coupling them togetherso to when rendered cective transmit s radio le signal identifying tiretairplane; receiving iaratus et s, ground station responsive to such liocode signal for when received communicatthat code signe-.l to e distantcontrol oiice; i means partly ot seid ground stotion ond rtly on euch ofe .plurolitg ci passing airplanes i ir'lcludinnY the transmitting meanson such ,rclity of eirpiones slid solo' receivingJ oppersfor renderingseid equipments o'o said oir- .nes eiective only one et o time in osequence ed by the respective eltitudes oi seid airplanes that time. i.in e system of the character described ior iorting the passage ofairplanes over o, ground tion; tronsmitting'meens nt the ground ste.- nnormally radiating; in limited aree over d station o, carrier' frequencyhaving distincc tone modulations relating to different nitiiesautomoticolly applied thereto successively e at o time; moons on eneirplsne including a, :lio receiver, e. radio transmitter ond en mtim ermeans for transmitting on e diiierent freency a reporting eignsl for olimited time only the modulation of tlie cerrler frequency rodiz by seidground stetion transmitting nieens rresponois with the altitude et whicht ot eirme is then flying es manifested by seid sitimer means; and menosincluding radio receiv-w g equipment et the ground station responsivesaid reporting signal and including communiting concretos forautomatically eonimunicet g to e, distont control oilce on indicationmonisting the nascose suon eirolcne ot suoli ',itude.

lli

9. lin e, oyster-n for eutozneticeily reporting to c, distont controloilice the vnascose of airplanes over o ground station, transmittingmeans at the ground ctetion normally ooeroting to radiate upwardlythroughout o zone ci limited extent o piurelity or radio lieems oidistinctive conrector one et o time in succession to designate diiierentaltitudes, radio receiving opperatus on @zich airplone eutorneticellyodjusted to be responsive to only one o1 seid radio beams novit-lg thechoreoter corresponding with the altitude at which that airplane istl'ien flying; radio frequency transmitter on the airplane having' itsoperation initiated by the response oi seid receiving or porotos forradiating ier limited time o, reporting sienel, und means et the groundstetion responsive to seid renoiting signal, whereby e. plurality ofail-plenos that may be passing over a, ground etntion at differentaltitudes will report their 'passage one et o, time es the groundstation transmitting menno successively creates the radio beams of thedistinctive characters corresponding with the respective .altitudes etwhich these eirplenes ore flying.

1G. A system 'lor reporting the identity und ps, sage of airplanes overo ground station compris ins', transmitting means et tile ground stationfor radiating over ein oren oi' limited extent shove the ground stotiono plurality of distinctive rcclio beams relating to different altitudesone et o time in succession, o radio receiver on each airplane foroperating en electro-responsive device, ineens including mi eitimeterfor controlling seid re ceiver to conse operation ci theelectro-responsive device onlyr in response to one distinctive radioboom correspomlincl with the altitude at which the airplane is thenflying', means on each aim-.lione including c radio transmitter and c.coding device .having its operation initiated by seid electro-responsivedevice for transmitting for e limited time e. reporting signal includingan oirplerle identifying code, ond means at said ground stotion forreceiving seid reporting signal and transmitting; t to o distant controloffice.

il. lin o, system for outomoticully reporting;r at e distant point thepsege o airplanes over a ground station, rodio transmitting moons et theground stotion including o scanner device normally rediotine' upwardlyover e limited ares. e. plurality oi initie-,ting rudio seems oidistinctive characters relating to different altitudes one at o. time insuccession, e. normelly inactive radio transmitter on each airplaneoperable when set into operation to send automatically a reportingsignal for e limited time, moons on the airplane for initiatingonerotion of seid transmitter in response to the reception oi aninitiating radio boem having the clncrecter corresponding with thealtitude et which the oil-plone is then flying, ond ineens ot the groundstation responsive to seid reporting siunels for transmitting to adistent point n code signol conforming with `the position of the scannerdevice et tile time a reporting signe-l received, whereby the altitudeoi esclu pessime' airplane is communicated to the dictons control point.

i2. "in on eutomctic airplane reporting system of tire characterdescribed, transmitting opparotus ot el ground static-n including erotary scanner normally operating to radiate upwardly over o zone oflimited ores e. carrier wave modulated with o plurality of distinctivetones one at o time es the econner roto/tes, means on ou airploneincluding en altitude detecting device for sending o radio signet on odiner-ent irequency paratus in response to the reception of a spaceradiation characteristic of the altitude in which the piene is thentravelling for causing the associated transmitting apparatus to transmita, radio sgnsi characteristic of the identity of the piane, means at theground station governed by the associated receiving apparatus forstopping operation oi' said scanning means during transmission from saidpiane, communication means associated with said ground station andgoverned in part by seid associated receiving apparatus and in part bysaid scanning means for transmitting to a distant station e. codecharacteristic of the identity of said plane, the altitude of said pianeend the identity of.' said ground station, and means on seid planegoverned by the associated apparatus for preventing a subsequentoperation oi the transmitting apparatus in response to the reception ofa radiation characteristic of its a1- 'titude for a predeterminedlimited time.

SmGWICK N. WEGHT. @SCAR S. I itl REFEBENQES (EXETER) The ioiiownsreferences are oi record in the 21e of this patent:

governed by its essocisted recei apv Number 22 UNTED STATES PAWNTS NameDate Marshall June 17, 1941 Muilerheim Jan. 27, 1992 Hershey Mar. 3,1942 Smith Feb. 9, 1932 Muether July 14, 1942 Hammond Mar. 13, 1934 LeshJan. 21, 1936 Wiiiiams Aug. 25, 1936 Sperry Mar. 4, 1930 Finnegan Apr.13, 1943 Janssen Nov. 18, 1941 Culbertson Oct. 1, 1940 Brown Mar. 12,1907 Hershey Apr, 30, 1935 Brixner Dec. 30, 1935 Ermes Dec. 23, 1930Buckley Jan. 10, 1933 Piastino Aug. 29, 1939 Luck Aug. 12, 1941 DunmoreMay 9, 1939 Kerr Feb. 16, 19113 Hershey Sept. 28, 1993

